This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 199 25 335.8, filed on Jun. 2, 1999, the entire disclosure of which is incorporated herein by reference.
The invention relates to a method of regulating the light transmission of an electrochromic glass pane, by generating an electrical voltage that is applied to the electrochromic glass pane and that is controlled dependent on the desired degree of light transmission, and by controlling the current that flows through the glass pane. The invention further relates to a circuit arrangement for implementing the method. Such electrochromic glass panes are especially suitable for use as the cockpit or cabin window panes of an aircraft, sunroofs and side windows of automobiles, and the like.
FIG. 1 shows a cross-section of a conventional electrochromic glass pane, which will simply be called an electrochromic glass herein. Two conventional glass panes 1, 2 are respectively arranged at each outer side of the electrochromic glass, and a transparent electrode layer 3, 4 is arranged directly adjacent to the respective glass panes 1, 2. A darkening or coloring layer 5, preferably a tungsten oxide layer, is arranged directly next to the transparent electrode layer 3. An electrolyte layer 6 and an ion storage layer 7 are arranged between the coloring layer 5 and the other transparent electrode layer 4. In order to vary the light transmission of such an electrochromic glass construction, the glass or its. components must be charged to a specific electrical potential. The voltage that is required to change the light transmission of the glass depends on the materials used. If a small electric potential exists between the electrodes 3, 4, then an ionic current flows into the, tungsten oxide layer. Electrons compensate the charge of the ions. The stored ions cause the originally transparent tungsten oxide layer to turn blue, thereby reducing the light transmission. This coloring or darkening effect can be reversed by shorting the circuit to reduce the voltage to zero or by applying a voltage of opposite polarity.
German Patent Laying-Open Publication DE 196 30 812 A1 discloses a transparent sunroof system for a vehicle. A transparent panel is slidably movable into an open position above or below another panel in the sunroof system in order to provide an opening in the roof. As a means of providing effective shade protection when the roof panel is closed and adequate transparency when the slidable panels are moved to an open position in which the panels are stacked one above the other, one of the two panels has an electrochromic layer that provides for variable light transmission or transparency. The transparency of the panel that is provided with the electrochromic layer can, for example, be varied by means of a variable resistor or potentiometer. Thus, for example, by applying a reduced voltage to a colored or darkened panel by means of the variable resistor, the panel can be xe2x80x9cbleachedxe2x80x9d, i.e., the transparency of the particular panel can be increased. Conversely, a transparent panel can be darkened or colored, i.e., the transparency can be decreased, by applying an increased voltage. According to this known technique, however, the increased voltage must be continuously applied to the glass without interruption, in order to maintain the reduced transparency condition. This is a disadvantage because the continuously applied higher voltage can have detrimental effects on the performance or service life of the glass, and requires increased energy, which is undesirable especially in a self-contained electrical system such as that of an automobile.
U. S. Pat. No. 5,384,578 (Lynam et al.) discloses a variable electrochromic light transmission system. The light transmission of a pane of glass is controlled by means of a memory time constant that is predetermined by the properties of the glass pane and a reference voltage set point. In this known system, the actual value of the light transmission is not determined, rather, the memory, time constant and the reference voltage set point control a drive signal or trigger signal that drives a multivibrator. The multivibrator generates a pulsed signal for charging the pane of glass.
In view of the above it is an object of the invention to provide a method of regulating the light transmission of an electrochromic glass that will optimize the electrical energy to be supplied to the electrochromic glass, with respect to magnitude and duration. It is a further object of the invention to provide a circuit arrangement for implementing the method according to the invention. The invention further aims to avoid or overcome the disadvantages of the prior art and to achieve additional advantages, as are apparent from the present specification.
The above objects have been achieved in a method of regulating light transmission of an electrochromic glass according to the invention, wherein the actual voltage existing or prevailing on the glass is determined and compared with a desired voltage value or reference voltage and, depending on the deviation or difference value of the actual voltage from the reference voltage, a control voltage of positive or negative polarity is applied to the glass to generate a control current flow. The control voltage remains applied until the actual voltage is substantially equal to the reference voltage. After the specified voltage level has been reached, the control voltage is switched off or reduced until no control current flows in the glass. Intermittently, at measuring intervals during a holding period, i.e., a period when there is no control current flow in the glass, the actual voltage on the glass is again measured and compared to the reference voltage or a threshold value. If it is determined that the actual value of the voltage on the glass deviates from the reference voltage by more than a predetermined threshold amount or value, then the control voltage is again applied to the glass with the appropriate polarity to minimize the deviation and is maintained until the actual voltage across the glass is again substantially equal to the reference voltage.
The method according to the invention provides the essential advantage that the appropriate reference voltages (with a defined current limit when applicable) and the time periods for the measuring intervals and charging or discharging periods are governed by the construction, the material, and the dimensions of the electrochromic glass. Thus, these parameters are adaptable to the specific electrochromic glass. A further advantage of the invention is that the automatic control or regulation electronics can be provided as an integrated component of the electrochromic glass or as a separate unit. The voltage supply for the automatic control or regulation electronics can be supplied, for example, by the on-board power supply network of an aircraft or by an automobile battery, or the like, depending on the particular application.
Embodiments of the invention provide that the control parameters, such as measuring intervals, voltage charging or discharging periods, and/or the reference voltages are variable during the automatic control operations. The automatic control operations may be carried out with discrete electronic components using threshold value queries or sampling and comparisons carried out by comparators. In a preferred embodiment, the automatic control is performed by a microcontroller or microprocessor that processes analog-to-digital converted signals using appropriate software to carry out the comparisons, timing, and other functions.
In an alternative embodiment of the invention, the light transmission of the glass, i.e. the charging or discharging of the glass, is regulated or controlled by measuring the control current flow in the glass, rather than by controlling the control voltage and the charging or discharging time period.
A circuit arrangement according to the invention for performing the method includes a computer or microprocessor, a power voltage follower, and a voltage reversing device. An input of the computer or microprocessor is connected via an analog-digital converter (A/D or ADC) to a component that provides a reference voltage set point, and an output of the computer or microprocessor is connected via a digital-analog converter (D/A or DAC) to the voltage follower and to the voltage reversing device. An output of the voltage reversing device is electrically connected to an input of the electrochromic glass. Also, the electrochromic glass as well as the voltage reversing device are connected via an analog-digital converter to an input of the computer or microprocessor.